drm/plane: Add new atomic_create_state callback

Commit 47b5ac7daa46 ("drm/atomic: Add new atomic_create_state callback
to drm_private_obj") introduced a new pattern for allocating drm object
states.

Instead of relying on the reset() callback, it created a new
atomic_create_state hook. This is helpful because reset is a bit
overloaded: it's used to create the initial software state, reset it,
but also reset the hardware.

It can also be used either at probe time, to create the initial state
and possibly reset the hardware to an expected default, but also during
suspend/resume.

Both these cases come with different expectations too: during the
initialization, we want to initialize all states, but during
suspend/resume, drm_private_states for example are expected to be kept
around.

reset() also isn't fallible, which makes it harder to handle
initialization errors properly. This is only really relevant for some
drivers though, since all the helpers for reset only create a new
state, and don't touch the hardware at all.

It was thus decided to create a new hook that would allocate and
initialize a pristine state without any side effect:
atomic_create_state to untangle a bit some of it, and to separate the
initialization with the actual reset one might need during a
suspend/resume.

Continue the transition to the new pattern with planes.

Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patch.msgid.link/20260526-drm-mode-config-init-v6-10-852346394200@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>

2 files changed, 18 insertions, 0 deletions

diff --git a/include/drm/drm_atomic_state_helper.h b/include/drm/drm_atomic_state_helper.h
index 691c1ccfa4e0..8d1ef268fdef 100644
--- a/include/drm/drm_atomic_state_helper.h
+++ b/include/drm/drm_atomic_state_helper.h
@@ -55,6 +55,8 @@ void drm_atomic_helper_crtc_destroy_state(struct drm_crtc *crtc,
 
 void __drm_atomic_helper_plane_state_init(struct drm_plane_state *state,
 					   struct drm_plane *plane);
+struct drm_plane_state *
+drm_atomic_helper_plane_create_state(struct drm_plane *plane);
 void __drm_atomic_helper_plane_reset(struct drm_plane *plane,
 				     struct drm_plane_state *state);
 void drm_atomic_helper_plane_reset(struct drm_plane *plane);
diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
index 419c88c873a6..2c5a5a70a71b 100644
--- a/include/drm/drm_plane.h
+++ b/include/drm/drm_plane.h
@@ -389,6 +389,22 @@ struct drm_plane_funcs {
 			    struct drm_property *property, uint64_t val);
 
 	/**
+	 * @atomic_create_state:
+	 *
+	 * Allocate a pristine, initialized, state for the plane object
+	 * and return it. This callback must have no side effects: in
+	 * particular, the returned state must not be assigned to the
+	 * object's state pointer and it must not affect the hardware
+	 * state.
+	 *
+	 * RETURNS:
+	 *
+	 * A new, pristine, plane state instance or an error pointer
+	 * on failure.
+	 */
+	struct drm_plane_state *(*atomic_create_state)(struct drm_plane *plane);
+
+	/**
 	 * @atomic_duplicate_state:
 	 *
 	 * Duplicate the current atomic state for this plane and return it.